Expression of major histocompatibility complex (MHC) class II genes is regulated primarily at the level of transcription. Aberrant or absent expression of these genes is associated with autoimmune disease and immunodeficiency, respectively. Characterizing the molecular mechanisms that regulate the transcription of these genes is critical for the development of new therapies and a greater understanding of the etiology of these diseases. The objective of the current application is to illuminate one such regulatory mechanism that has not been addressed: the role of chromatin structure and its remodeling in MHC class II gene transcription. Based upon previous evidence, it is hypothesized that there are two chromatin "barriers"--one on the promoters and the second on the protein coding regions--present on MHC class II genes. The first specific aim will employ restriction endonuclease accessibility and micrococcal nuclease assay to characterize the changes in chromatin structure on MHC class II genes associated with transcriptional activation of these genes. In addition, the role gene-specific trans-acting factors in mediating the changes in chromatin structure will be addressed. Recent observations indicate that one of these trans-acting factors, the class II trans-activator (CIITA) functionally interacts with a subunit of the chromatin remodeling complex SWI/SNF. In the second specific aim, protein interaction assays will be used to characterize the domain of CIITA required for binding to SWI/SNF. Once identified, this domain will be used to determine the functional significance of CIITA-SWI/SNF interaction, in terms of chromatin remodeling and transcriptional activation. CIITA has been found to have endogenous histone acetyltransferase activity, in addition to its ability to recruit at least two histone acetyltransferase enzymes. In the third specific aim, the relationship between CIITA mediated histone acetylation of nucleosomes on MHC class II genes, and SWI/SNF mediated chromatin remodeling will be addressed. Relative changes in transcriptional activation and chromatin remodeling will be determined in cell culture models in which the recruitment of SWI/SNF and CIITA mediated histone acetylation are manipulated. Through these specific aims the importance and mechanistic basis of chromatin remodeling in the transcription of MHC class II genes will be determined.